From both a cost and a maintenance point of view, it has become increasingly desirable to mold complicated configurations, such as ventilator grills from plastic rather than assembling them from metal stampings. Also, this arrangement has aesthetic advantages. However, the use of molded plastic for this type of product has been considered disadvantageous from the point of view of cost. The size of the openings to which ventilators of this type are applied varies substantially from one boat design to another. In part, this is due to differences in air flow requirements of various size engines and differences in the design of the engine compartment itself. Also, in some cases, aesthetics are in influencing factor on the size of the grill. In the case of metal grills, while this problem was a nuisance, it was not a substantial cost factor because these grills were either assembled for a number of separate components or the dies from which they were stamped were less expensive than molds for a plastic product of comparable size. With molded plastic grills, because each size of grill has required a separate mold, good only for making that particular grill size the investment in tooling has been very high. Since these grills are of substantial size, the cost of the molds was, for all practical purposes, prohibitive, unless there was a particular size with a large volume demand. The invention has as a primary objective a grill construction which materially reduces mold costs without sacrifice of the grills' ornamental and functional characteristics. The invention also makes it possible to satisfy the requirements of ventilator openings of a variety of sizes, all having the same basic ornamental exterior appearance.